The only genre in music where full-length albums are based on covers is jazz, as it seems to me.

What?

I mean that many jazz albums consists of interpretations of classic themes, so-called jazz-standards, and while jazz musician releases album where four of eight compositions are standards like "On The Sunny Side Of The Street" or "Caravan", and it is ok, metal albums with such proportion of covers and originals would be nonsense.

Most jazz artists rarely do this, unless it's like, pussy jazz for white people. I would say that most jazz musicians are more creative than this, and even if they're covering a standard they'll put their own stamp on it, reinterpret it to make it their own.

Deathevokation's cover of an Antropomorphia song as the next-to-last track on The Chalice of Ages is another example of a well-executed/placed cover song on an album. By putting their own stamp on it, the song fits naturally into the flow of the album, so much so that I suspect many people probably don't even realize it's a cover._________________Good deals with: Numerator41, addison, deathsleep, witch sermon, xyosefx, invinCIBility (4X), Weltbrand (2X), DrkKnight, K-mart (2X), drinks, LifeDepraved

"Necromantical Screams" on Dying Emotions Domain by Astrofaes.
"Kingdom Against Kingdom" on Inferno of Sacred Destruction by Black Witchery.
"Solitude" on Shadows of the Sun by Ulver.
"Manic Depression" on Retaliation by Carnivore.

I'm also partial towards "Set the Controls for the Heart of the Sun" on Revelations of the Black Flame by 1349. It's not particularly mind-blowing, though...